ethtool: add PAUSE_NTF notification

Send ETHTOOL_MSG_PAUSE_NTF notification whenever pause parameters of
a network device are modified using ETHTOOL_MSG_PAUSE_SET netlink message
or ETHTOOL_SPAUSEPARAM ioctl request.

Signed-off-by: Michal Kubecek <mkubecek@suse.cz>
Signed-off-by: David S. Miller <davem@davemloft.net>